Analog Devices SSM2167 Installation and operating instructions

AN-583
APPLICATION NOTE
One Technology Way •P. O. Box 9106 •Norwood, MA 02062-9106, U.S.A. •Tel: [phone] •Fax: [phone] •www.analog.com
Evaluating the SSM2167 Low Voltage Microphone Preamplifier with Variable
Compression and Noise Gating
by Shawn Scarlett
Rev. D | Page 1 of 4
THE SSM2167 EVALUATION BOARD
The SSM2167 evaluation board is a convenient means to
evaluate and understand the operation of the SSM2167. This
application note provides a basic explanation of how the board
is set up, and how to use it to evaluate the SSM2167. This
document is only a supplement and refers to figures contained
in the SSM2167 data sheet.
This application note also contains the schematics and layout for
the SSM2167 evaluation board to allow easy modification and
experimentation. Applications support is available from Analog
Devices, Inc., online at www.analog.com or in the United States
at 1-800-ANALOGD or 1-800-262-5643.
BASIC CONNECTIONS AND SETUP
The SSM2167 board features simple, easy-to-use connections
that allow for a broad range of experimentation. The evaluation
board is available only with the SSM2167-1.
Power and Ground
The SSM2167 is optimized for operation at 3 V; however, it can
operate from a wide range of supplies. Refer to the SSM2167 data
sheet for the maximum limits. The SSM2167 evaluation board
can be connected to a bench power supply or two AA batteries.
Power leads must be soldered into place at JP3. Alternatively, a
header jack can be soldered to the SSM2167 board to allow easy
disconnection. The power and ground connections are critical
to the performance of the SSM2167 board; therefore, ensure
proper connection.
Shutdown Connection
The low current shutdown current connection is located at the
lower part of the SSM2167 evaluation board along with the
power and ground. The SSM2167 board has a pull-up resistor
installed so that if no connection is made at that point, the device
operates in active mode. To enable the shutdown feature, connect
SD to ground. To perform an in-depth analysis on the shutdown
current, remove the pull-up resistor (R5). Do not leave the
shutdown pin floating. When R5 is removed, connect SD
directly to the supply or ground.
Signal Connections, Input, and Output
Signal sources can be connected to the SSM2167 evaluation
board with standard 3.5 mm jacks or leads, which can be
soldered directly to the SSM2167 evaluation board at JP1 and
JP2. The SSM2167 evaluation board uses 3.5 mm stereo sockets
with the signal on the tip and the sleeve connected to the board
ground; the ring is left floating. At both jumper connections, a
ground point is available to prevent noise.
The input jack is configured for maximum versatility. By
default, it is designed for use with an electret microphone or
input source. It can be changed easily to accommodate dynamic
microphones.
ELECTRET MICROPHONES
The SSM2167 evaluation board is configured with a 2.2 kΩ
resistor (R4) to the supply for use as a biasing resistor. It connects
directly to the signal path so that both the jack and the jumper
(JP2) can be used as input connections. Standard computer electret
microphones can be used without modification because the ring
and tip are connected internally in the microphone. The input jack
and JP2 are decoupled from the input pin via a 0.1 µF capacitor (C1).
DYNAMIC MICROPHONES
When the SSM2167 evaluation board is used with a dynamic or
self-powered microphone, remove R4.
OUTPUT SIGNAL
The output jack is decoupled from the circuit via a 10 µF capacitor
(C2). The connection can be made at either JP1 or the standard
3.5 mm jack, with the signal connection to the tip of the plug.
For listening tests, the output signal can be connected directly
from the 3.5 mm jack to an RCA input on a normal audio
amplifier using a standard stereo adapter cable. In this case, use
the left (white or black) RCA connection because it corresponds
with the tip of the 3.5 mm jack. The output of the SSM2167 is
not sufficient to drive headphones or other output transducers
without external amplification.

AN-583 Application Note
Rev. D | Page 2 of 4
TEST EQUIPMENT SETUP
The recommended equipment and configuration is shown in
Figure 1. A low noise audio generator with a smooth output
adjustment range of 50 μV to 50 mV is a suitable signal source.
A 40 dB pad is useful to reduce the level of most generators by
100´ to simulate microphone levels. The input voltmeter can be
connected before the pad and only needs to go down to 10 mV.
The output voltmeter must go up to 2 V. The oscilloscope is
used to verify that the output is sinusoidal, that no clipping
occurs in the buffer, and that the noise gating threshold is set.
OSCILLOSCOPE
AC VOLTMETERAC VOLTMETER
SIGNAL
GENERATOR SSM2167
EVALUATION
BOARD
02728-001
Figure 1. Test Equipment Setup
CONNECTIONS
Connect power, ground, input, and output as described in the
Basic Connections and Setup section.
TEST SETUP
To confirm the operation of the board and test setup, first put
JP4 in the 1:1 position and JP5 in the −55 dB position. With
power on, adjust the generator for an input level of 15 mV,
1 kHz. The output meter should indicate approximately
100 mV. If it does not, check the setup.
LISTENING
Connect a microphone to the SSM2167 and listen to the results.
Ensure proper power for the microphone by following instructions
in the Basic Connections and Setup section. Experiment with
the settings to hear how the results change. The compression
ratio keeps the output steady over a range of source to microphone
distances, and the noise gate keeps the background sounds subdued.
SETTING THE NOISE GATE THRESHOLD
The SSM2167 evaluation board provides three different preset
values of noise gate threshold. Experiment with these values by
varying the gate. The SSM2167 evaluation board also provides
landing pads for a custom value that can be extrapolated from
the specifications table in the SSM2167 data sheet, or the noise
gate vs. RGATE figure the SSM2167 data sheet. Using more than
5 kΩ is not recommended because extremely low noise gate
thresholds may approach the noise floor of the system.
The highest setting (−48 dB) is recommended to start an evaluation.
If the input signal is not sufficient to surpass the threshold,
lower the setting. In most applications, the input signal easily
overcomes this setting. If the gate is set too low, the background
noise is amplified well into the audible range. By examining the
function (see the general input/output characteristics figure in
the SSM2167 data sheet), the maximum gain of the device can
be determined when the input signal is at the noise gate threshold.
The dashed line on the transfer function represents unity gain;
the distance between the dashed line and the solid line represents
the VCA gain.
ADJUSTING THE COMPRESSION RATIO
The SSM2167 evaluation board provides three different settings
for the compression ratio in the same manner as the noise gate
threshold. Experiment with different compression ratios to
determine what sounds best in a given system; starting with a
2:1 ratio is recommended. High compression ratios exaggerate
the effect of the noise gate because the compression ratio
determines the gain at the noise gate, as shown in the output vs.
input characteristics figure in the SSM2167 data sheet. Use
compression of 10:1 only in systems where the noise floor is
well below the noise gate. Most systems require between 2:1
and 5:1 compression for best results.
LISTENING TEST
The final step in evaluating the SSM2167 is a listening test.
The improvement in vocal clarity can be heard by recording
the SSM2167 output or listening to it live. Ideally, connect the
SSM2167 evaluation board to an existing system. The impact
of the compression is demonstrated by shorting out RCOMP
(R9 through R12). When the RCOMP resistor is shorted, the
VCA reverts to the audible 1:1 compression setting, which does
not affect the noise gate or limiting settings. The effect of
turning off the compression is most noticeable when the input
signal is between −50 dBV and −40 dBV. Evaluating the SSM2167
within the end application also gives the best indication of how
high the noise gate threshold should be set. The noise level of
the system is greatly influenced by the design of the system,
including cooling fans, hard drives, handling, and other sources
of acoustic noise.
Listening tests are the most critical part of an evaluation. Because
test equipment and signal generators do not represent audio
signals well, listening is the best way to evaluate the benefits of
the SSM2167. The SSM2167 evaluation board makes it easy to
implement the SSM2167 and to pick appropriate application
settings. The end result is a noticeable improvement in signal
clarity and a system that is easy for customers to use.
02728-002
Figure 2. SSM2167 Evaluation Board; Top Layer Including Component
Identification and Placement

Application Note AN-583
Rev. D | Page 3 of 4
02728-003
Figure 3. SSM2167 Evaluation Board; Top Layer
02728-004
Figure 4. SSM2167 Evaluation Board; Bottom Layer
500K
SSM2167-1RMZ
10K
10UF
BLK
BLU RED
10-89-7102
0.1UF
10UF
0.1UF
174K 75K 15K
0
DNI
3K 2K 1K
0
10UF
10UF
DNI
DNI
GRY
SSW-102-01-G-S
DNI
10-89-7102
1000PF
2.2K
10UF
DNI
DNI
SSW-102-01-G-S
DNI
SJ1-3525NG
DNI
10UF
SJ1-3525NG
100K
GRY
10UF
DNI
10UF
INPUT
OUTPUT
SDGND+3V
R9
R5
C11
C10
C1
C6
C5
C4
C8 C7
C9
C2
R12
R16
U1
JP1
JP2
JP5
JP4
C3
R4
R7
R8
R10 R11
R13 R14 R15
J2
J1
SD
3.3V
3.3V
3.3V
SD
3.3V
3.3V
3.3V
3.3V
1
1
1 1 1
NP
NP
10
2
39
5
1
7
8
46
2
1
2
1
10987 65 43 21
10987 65 4
321
NP
5
4
3
2
1
5
4
3
2
1
AGND
AGND
AGND
AGND
AGND
AGND
AGND
AGND
AGND
AGND
AGND AGND
VDD
OUTPUT
COMPRESSION_RATIO
GATE_THRS
AVG_CAPINPUT
BUFOUT
SHUTDOWN_N
VCAIN
GND
02728-005
Figure 5. SSM2167 Evaluation Board Circuit Schematic

AN-583 Application Note
Rev. D | Page 4 of 4
Table 1. Parts List for SSM2167 Evaluation Board
Reference Description Part Number Value Tolerance (%)
U1 Low voltage microphone pre-amp SSM2167-1RMZ SSM2167-1RMZ Not applicable
C1, C10 Chip capacitors, X7R, 0805 GRM21BR71H104KA01L 0.1 µF 10
C2, C3, C9 Tantalum capacitors TAJA106K010RNJ 10 µF 10
C4 Capacitor, ceramic monolithic, X5R GRM31CR61E106KA12L 10 µF 10
C11 Capacitor, ceramic, C0G GRM2165C1H102JA01D Do not install 5
C5 to C8 Capacitors, ceramic, X7R GRM21BR71A106ME51 Do not install 20
J1, J2 3.5 mm stereo jacks SJ1-3525NG SJ1-3525NG Not applicable
JP4, JP5 Headers 10-89-7102 10-89-7102 Not applicable
JP4, JP5 Shunt connector SNT-100-BK-G SNT-100-BK-G Not applicable
JP1, JP2 Headers SSW-102-01-G-S Do not install Not applicable
R10 Resistor, precision thick film chip, R0805 ERJ-6ENF7502V 75 kΩ 1
R11 Resistor film, SMD, 0805 MC 0.1W 0805 1% 15K. 15 kΩ 1
R13 Resistor chip, 0805 MC0805S8F3001T5E 3 kΩ 1
R14 Resistor, precision thick film chip, R0805 ERJ-6ENF2001V 2 kΩ 1
R15 Resistor, precision thick film chip, R0805 ERJ-6ENF1001V 1 kΩ 1
R12, R16
Resistors, thick film chip
ERJ-6GEY0R00V
Do not install
Not applicable
R4 Resistor film, SMD, 0805 MC 0.1W 0805 1% 2K2. 2.2 kΩ 1
R5 Resistor, high precision thick film chip PHT0805Y5003BGT200 500 kΩ 0.1
R7 Resistor, precision thick film chip, R0805 ERJ-6ENF1003V 100 kΩ 1
R8 Resistor, precision thick film chip, R0805 ERJ-6ENF1002V 10 kΩ 1
R9
Resistor, precision thick film chip
ERJ-6ENF1743V
174 kΩ
1
+3V Test point TP-104-01-02 RED Not applicable
SD Test point TP104-01-06 BLU Not applicable
GND Test point TP-104-01-00 BLK Not applicable
INPUT, OUTPUT Test point TP104-01-08 GRY Not applicable
REVISION HISTORY
10/15—Rev. C to Rev. D
Changes to Title, Shutdown Connection Section, and Signal
Connections, Input, and Output Section ...................................... 1
Changes to Figure 2.......................................................................... 2
Changes to Figure 3, Figure 4, and Figure 5.................................. 3
Changes to Table 1 ............................................................................ 4
2/13—Rev. B to Rev. C
Changes to Figure 5.......................................................................... 3
Changes to Table 1............................................................................ 4
©2002–2015 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
AN02728-0-10/15(D)